The configuration u have can work. The reason u need GY240 or any Heading Hold Gyro is because your TX do not have Revo mixing. If u have Revo mixing, u have an option to go either :
1 - Heading Hold and turn off Revo mixing.
2 - Normal Gyro with Revo Mixing.

U can either go 50% brushless (main motor is brushless or tail is brushless only) or 100% brushless (Both tail and main is brushless). Good thing of going brushless is it is more powerful than dual motor or direct drive (if u make your own CDROM motor for tail properly) and close to or maintainance free.

I would lean toward 3 cell LiPos. Especially if you stay brushed. The GY240 is heavy, and 2 cell LiPos are a low voltage pack. 3 cell LiPos will give you lots of power. Yes, this makes for short tail motor life if you use a low frequency tail ESC. For a bit more money, get a schulze slim 105he tail ESC. This high frequency controller eases the abuse that we put the tail motors through. Brother #1 flew his Piccolo for over a year before his first tail motor went. Maybe not quite a thousant packs, but a LOT. All on 3 cells LiPos. Schulze slim 105he.

Oh, the Pixie 7P is programmed form the transmitter, through a series of throttle commands. (no USB needed)

I found the regular noob-brushless-kit from gobrushless.com and the HiMax 2015 (4100) at helihobby and like either one paired with a CC Phoenix 10 and a GY240. (a CC Pixie 7P to do the tail). Sound like a good idea to me!

But will this hover nicely with my E-Tec 2cell 1200mA or do I need more power? Can I keep the existing receiver or do I need a new one? If a new one, which one? Do they all work with 2 and 3 cell LiPos?

@Geoffrey
I read through that pages and got all over planes, anchors, magnets, shafts and really going crazy! What I am looking for is not a answer in 2 sentences but as I am a newbie I get very much confused but 20 pages of brushless issues. Can't "we" put that in a nutshell? Like some issues I started e.g. going brushless or switching to another TX etc. (or course related to our microhelis and not related to all RC).

@Geoffrey
Not easy bro. But easier to follow. Everybody entering a new topic needs to aquire a lot of information. Some of it is easy to get and some of it is hard to get. That's where I am. And I am not even native english so it's sometimes extremly hard to understand what you guys are talking about

The thread I started "Micro Heli Setup Listing (add yours) " is one of this places where I don't get the "how" but the "who" and the "what". It's my way to gather information. Get tons of examples and try to derivate the formulas...